Apparatus and method for controlled delivery of a gas

ABSTRACT

Disclosed are apparatus for delivery of a gas, e.g., carbon dioxide and/or chlorine dioxide, and methods of its use and manufacture. The apparatus includes an envelope, and a sachet within the envelope that contains reactant, which generates a gas in the presence of an initiating agent, e.g., water. The envelope allows release of the gas from the envelope. In another embodiment, the apparatus includes an envelope and a partition that separates two reactants within the envelope. The envelope allows an initiating agent into the envelope and release of the gas generated by the reactants in the presence of the initiating agent.

[0001] RELATED APPLICATIONS

[0002] This application claims priority to copending U.S. ProvisionalPatent Application Serial. No. 60/190,028, filed Mar. 17, 2000, and No.60/183,368, filed Feb. 18, 2000, the entire disclosures of which arehereby incorporated by reference herein.

FIELD OF THE INVENTION

[0003] The invention relates generally to apparatus and methods fordelivery of a gas and more specifically to apparatus and methods forcontrolling the amount, rate and duration of gas delivery.

BACKGROUND OF THE INVENTION

[0004] The use of gas for retarding, controlling, killing or preventingmicrobiological contamination (e.g., bacteria, fungi, viruses, moldspores, algae and protozoa); retarding, preventing, or controllingbiochemical decomposition; controlling respiration, deodorizing and/orretarding and preventing chemotaxis to name a few, is known. Such gasesinclude, but are not limited to, chlorine dioxide, sulfur dioxide,nitrogen dioxide, nitric oxide, nitrous oxide, carbon dioxide, hydrogensulfide, hydrocyanic acid, and dichlorine monoxide. For example, the useand efficacy of chlorine dioxide is documented and discussed in variouspublications such as G. D. Simpson et al., A Focus on Chlorine Dioxide,An Ideal Biocide (visited Feb. 5, 2000)http://clo2.com/readings/waste/corrosion.html, and K. K. Krause, DDS etal., The Effectiveness of Chlorine Dioxide in the Barrier System(visited Feb. 5, 2000) http://www.dentallogic.com/dentist/effects.htm.

[0005] In particular, chlorine dioxide has been found to be useful as adisinfectant, antiseptic and sanitizer. It is used, e.g., to disinfectdrinking water and various water supplies. In addition, chlorine dioxidefinds use as a bleaching agent for flour, fats and textiles. Chlorinedioxide also has shown great utility as an antiseptic for treating metaland plastic surfaces, as well as other substrates such as countertops,meat processing and packaging equipment, and dental and medicalinstruments and devices.

[0006] One disadvantage of the prior art methods for generating chlorinedioxide gas generally is that unsatisfactory levels of by-products orreactants remain as a residue. For example, in the case of chlorinedioxide gas, the byproduct chlorite leaves residues on food handlingequipment and medical and dental surfaces. Human contact with suchresidues should be avoided or substantially minimized according to FDAand EPA regulations.

[0007] Another requirement in the food handling and related industriesis the need for raw materials or ingredients that are safe to handle inthe preparation of the disinfectant. The requirement is for theinclusion of reagents that are safe to use and, after generatingchlorine dioxide, produce side products that are non-toxic and/orbiodegradable.

[0008] Also, although it has great beneficial characteristics, chlorinedioxide can not be transported commercially as a concentrated gas forits use and instead has been generated at the site where it is used.Thus, an on-site gas generation plant typically is required to generatethe gas that is then delivered to the fluid in which it will be used.Such apparatus takes up space and represents a significant addedexpense. Moreover, even when prior art apparatus do not require aseparate gas generation component e.g., those shown in European PatentPublication No. 0 571 228 for sulfur dioxide generation, such apparatusare still undesirable because controlling the amount of gas generated,the efficiency of the generation, and the duration of the gas generationhas proven difficult, if not unsuccessful.

[0009] There exists a need for the controlled, on-site generation ofgases, such as sulfur dioxide and chlorine dioxide, which can beproduced safely, efficiently and economically, without the necessity fora separate generation plant or unwanted by-products. The presentinvention addresses these needs.

SUMMARY OF THE INVENTION

[0010] A novel approach to the delivery of gas has now been discovered.The present invention uses a unique delivery system that controls therate and efficiency of gas-producing reactions. Moreover, by usingdiscreet amounts of reactant contained within a multi-layered apparatus,the skilled practitioner can now fabricate a gas delivery apparatus thatis compact, cost-effective and safe. Furthermore, the present inventioncan be used for a variety of applications, including delivery of gas toair or water, for a variety of purposes including disinfection,deodorization, bleaching and sanitization.

[0011] In one aspect, the present invention features an apparatus fordelivery of a gas. An exemplary embodiment of this apparatus generallyincludes an envelope, a sachet disposed within the envelope, and areactant disposed within the sachet that generates a gas in the presenceof an initiating agent, wherein the envelope allows release of the gasfrom the envelope.

[0012] One currently preferred embodiment of the invention features anapparatus for delivery of a gas which includes a first reactant disposedwithin a first sachet, a second reactant disposed within a secondsachet, a third sachet disposed about the first sachet and the secondsachet, an envelope disposed about the third sachet, a frangible pouchdisposed within the envelope adjacent to the third sachet, and aninitiating agent disposed within the frangible pouch. In thisembodiment, the first reactant and the second reactant generate a gas inthe presence of the initiating agent, and the envelope allows release ofthe gas from the apparatus.

[0013] In a third exemplary embodiment, the apparatus for delivery of agas includes an envelope, a partition disposed within the envelopedefining a first volume and a second volume, a first reactant disposedin the first volume, and a second reactant disposed within the secondvolume. In this preferred embodiment, the first reactant and the secondreactant generate a gas in the presence of an initiating agent, and theenvelope allows entry of the initiating agent into the apparatus.

[0014] In another embodiment, the apparatus for delivery of a gasincludes a sachet and a reactant disposed within the sachet thatgenerates a gas in the presence of an initiating agent. In thisembodiment, the sachet allows contact of the initiating agent with thereactant and release of the gas from the apparatus.

[0015] In another aspect, the present invention features a method offorming an apparatus for delivery of a gas including the steps of (a)providing a multi-layer structure comprising a reactant layer centrallydisposed between two sachet layers, and two envelope layers disposedadjacent to the two sachet layers such that the two sachet layers arecentrally disposed between the two envelope layers, and (b) stamping themulti-layer structure such that the two envelope layers form an envelopedefined about its perimeter by the stamp, and the two sachet layers forma sachet defined about its perimeter by the stamp.

[0016] In yet another aspect, the present invention features a method ofdelivering lo gas including the steps of (a) providing an apparatus fordelivery of a gas comprising: an envelope, a sachet disposed within theenvelope, and a reactant disposed within the sachet that generates a gasin the presence of an initiating agent, wherein the envelope allowsrelease of the gas from the envelope; and (b) disposing the apparatus inan environment that comprises an initiating agent. The environment canbe liquid and the initiating agent can be water. Alternatively, theenvironment can be gaseous and the initiating agent can be water vapor.

[0017] In short, the invention provides the art with a heretoforeunappreciated method and apparatus for the controlled generation of agas. Moreover, in accordance with the present teachings, the inventioncan also readily be applied to the generation of a liquid.

[0018] The invention will be understood further upon consideration ofthe following drawings, description and claims.

DESCRIPTION OF THE DRAWINGS

[0019] The invention is pointed out with particularity in the appendedclaims. The drawings are not necessarily to scale, emphasis insteadgenerally being placed upon illustrating the principles of theinvention. The advantages of the invention described above, as well asfurther advantages of the invention, can be better understood byreference to the description taken in conjunction with the accompanyingdrawings, in which:

[0020]FIGS. 1A and 1B are a perspective view and a cross-sectional sideview, respectively, of an embodiment of an apparatus constructed inaccordance with the present invention;

[0021]FIGS. 2A and 2B are a perspective view and a cross-sectional sideview, respectively, of another embodiment of an apparatus constructed inaccordance with the present invention;

[0022]FIGS. 3A and 3B are a perspective view and a cross-sectional sideview, respectively, of yet another embodiment of an apparatusconstructed in accordance with the present invention;

[0023]FIGS. 4A and 4B are a perspective view and a cross-sectional sideview, respectively, of still yet another embodiment of an apparatusconstructed in accordance with the present invention;

[0024]FIGS. 5A and 5B are a perspective view and a cross-sectional sideview, respectively, of still yet another embodiment of an apparatusconstructed in accordance with the present invention

[0025]FIG. 6 is a graph depicting gas concentration versus timecomparing exemplary apparatus fabricated with and without an envelope;

[0026]FIG. 7 is a graph depicting gas concentration versus timecomparing exemplary apparatus fabricated with envelope materials havingdifferent vapor transmission rates;

[0027]FIG. 8 is a graph depicting gas concentration versus timecomparing exemplary apparatus fabricated with and without a sachet;

[0028]FIG. 9 is a graph depicting gas concentration versus timecomparing exemplary apparatus fabricated with extruded and wovensachets;

[0029]FIG. 10 is a graph depicting gas generation versus time comparingexemplary apparatus fabricated with sachets made of materials havinghydrophobic and hydrophilic surfaces; and

[0030]FIG. 11 is a graph depicting gas concentration versus timecomparing exemplary apparatus fabricated with different reactant ratios.

DETAILED DESCRIPTION OF THE INVENTION

[0031] A novel approach to the delivery of gas has now been discovered.By using discrete amounts of reactant contained within a multi-layeredapparatus, the skilled practitioner can now fabricate a gas deliveryapparatus that is compact, cost-effective, and safe. The presentinvention can be used for a variety of applications, including deliveryof gas to air or water, for a variety of purposes includingdisinfection, deodorization, bleaching and sanitization.

[0032] One advantage to this approach is that gas can be generatedwithout the need for mechanical equipment, thus freeing up any spacesuch mechanical equipment would require. Another advantage is that thereactants, which can be dangerous to handle directly, are isolated fromcontact with the user by the layers, which enclose the reactant.

[0033] Another advantage is that the apparatus of the present inventiondoes not allow for the dilution of the reactant. Because the reactantremains concentrated within the sachet, less reactant is necessary todrive the reaction to completion and the reaction is more efficient thanit would be if the reactants were diluted. Furthermore, because thereaction is driven to completion, unreacted reactant is minimized oreliminated. The reactant concentration also minimizes unwantedby-products.

[0034] Yet another advantage is that the apparatus is small andtherefore can be easily and economically shipped and administered. Yetanother advantage is that the apparatus can be manipulated to allow foreither rapid or slow delivery of gas. Another advantage is that theapparatus can be designed to deliver gas to either a gas, e.g., air, ora liquid, e.g., water. Other advantages will be evident to thepractitioner having ordinary skill in the art.

[0035] In order to more clearly and concisely describe the subjectmatter of the claims, the following definitions are intended to provideguidance as to the meaning of specific terms used in the followingwritten description, examples and appended claims.

[0036] As used herein the term “sachet” means a closed receptacle forreactant. The sachet is “closed” in the sense that the reactants aresubstantially retained within the sachet and the sachet volume issubstantially sealed around its perimeter. However, the material ormaterials used to construct the sachet are chosen to allow entry of theinitiating agent and exit of the gas generated. The material ormaterials used to construct sachets are referred to herein as “sachetlayers.” Sachet layers typically are constructed from a planar material,such as a polymeric sheet or film. Preferred materials for sachet layersare described in greater detail below. Relying upon the teachingdisclosed herein, and the general knowledge in the art, the practitionerof ordinary skill will require only routine experimentation to identifyone or more sachet layers and/or construct one or more sachets adaptedfor the purpose at hand.

[0037] As used herein the term “envelope” means a closed receptaclewherein the envelope volume is sealed substantially about its perimeter,which contains at least one sachet and allows release of the gas fromthe envelope. The material or materials used to construct envelopes arereferred to herein as “envelope layers.” Envelope layers typicallycomprise a planar material such as a sheet or film, including, but notlimited to perforated films, non-perforated films and membranes.Preferred materials for envelope layers are described in greater detailbelow. Relying upon the teaching disclosed herein, and the generalknowledge in the art, the practitioner of ordinary skill will requireonly routine experimentation to identify one or more envelope layersand/or construct one or more envelopes adapted for the purpose at hand.

[0038] As used herein “reactant” means a reactant or a mixture ofreactants that generate gas in the presence of an initiating agent.

[0039] For purposes of the present invention, initiating agent includes,but is not limited to, gaseous or liquid water. For example, for drybiocidal applications of the present invention, such as for thereduction of molds when shipping fruit, moisture in the atmosphere canbe used as an initiating agent. The term “dry application” for thepurposes of this application means at least an application where theapparatus of the present invention is not immersed in water or any otherliquid. The term “wet application” for the purposes of the presentinvention means at least an application where the apparatus of thepresent invention is immersed in water, or other liquid, which canoptionally include water. For wet biocidal applications, i.e., when theapparatus of the present invention is immersed in water or any otheraqueous medium, such as that used for disinfecting dental or foodequipment, the water in which the apparatus is immersed can be used asthe initiating agent. Alternatively, the initiating agent can beincluded within the apparatus, e.g., contained in a frangible pouchdisposed to within the apparatus.

[0040] Generation of a gas, e.g., by acid activation, is well known inthe art. For example, chlorine dioxide (ClO₂₎ is generated from sodiumchlorite and an acid, such as citric acid, in the presence of moistureas follows.

5 ClO₂ ⁻+4 H⁺⇄4 ClO₂+2 H₂O+Cl⁻  (I)

ClO₂ ⁻→ClO₂+e⁻  (II)

[0041] Specific examples of this reaction include the following.

2 NaClO₂+Na₂S₂O₈→2 ClO₂+2 Na₂SO₄  (III)

2 NaClO₂+NaOCl+HCl→2 ClO₂+2 NaCl+NaOH  (IV)

[0042] Alternatively, chlorine dioxide can be produced by the reductionof a chlorate, e.g., sodium chlorate or potassium chlorate, in thepresence of an acid, e.g., oxalic acid. Generally the reaction occurs asfollows.

ClO₃ ⁻+2H⁺+e⁻→ClO₂+H₂O  (V)

[0043] For example, reduction of sodium chlorate by acidification in thepresence of oxalic acid to produce chlorine dioxide can proceed asfollows.

2 NaClO₃+H₂C₂O₄→2 ClO₂+2 CO₂+2 H₂O  (VI)

[0044] Another example of generation of a gas by acid activation is theactivation of a sulfite, e.g., sodium bisulfite or potassium bisulfite,with an acid, e.g., fumaric acid and/or potassium bitartrate, in thepresence of moisture to form sulfur dioxide.

NaHSO₄+4H⁺⇄SO₂+2 H₂O+Na⁺  (VII)

[0045] Yet another example is the acid activation of a carbonate, e.g.,calcium carbonate with an acid, e.g., citric acid, to formt carbondioxide.

CaCO₃+2H⁺⇄CO₂+H₂O+Ca⁺  (VIII)

[0046] Other applications will be apparent to the skilled practitioner.For example, the generation of nitrogen dioxide by the acid activationof a nitrite, e.g., sodium nitrite or potassium nitrite. Alternativeroutes for generation of a gas, e.g., reduction of chlorates by sulfurdioxide (Mathieson Process), are well known in the art and can beutilized in accordance with the present invention.

[0047] The present invention can be used in a wide variety ofapplications. For example, chlorine dioxide can be used for thedisinfection of water, e.g., municipal water treatment: as adisinfectant for foods, beverages, fruits and vegetables; and for thecleaning and disinfection of medical, dental and food equipment.Chlorine-dioxide has been shown to be an effective disinfectant atconcentrations as low as 0.2 mg/L. Chlorine dioxide is a desirablereplacement for chlorine, the traditional water treatment chemical,because it has been found to inactivate microbes at lower levels andover a wider pH range. For example, chlorine dioxide can be used toreduce or eliminate biofilms because it penetrates the cell wall ofnaturally occurring, colony-building microorganisms and disrupts theproteins necessary for reproduction. Moreover, chlorine dioxide does notproduce chlorinate by-products, e.g., trihalomethanes. Moreover, it hasbeen found to be active against pathogens that are resistant tochlorine. It can be used as a slimicide in paper or pulp machines, forwastewater treatment, and for industrial water treatment, e.g., coolingor recycle streams. It can be used for odor control or as an aerialbiocide and virucide. It can be used for the treatment of sulfides inthe oil industry, for industrial cleaning, e.g., circuit boardcleansing, and for paper or tallow bleaching. Sulfur dioxide also has avariety of uses, such as a mold and fungus inhibitor for use in shippingand storing fruits and vegetables. Based on the teachings disclosedherein the practitioner of ordinary skill will appreciate the numerousother applications for which the present invention can be used andprovides a heretofore unmet need.

[0048] The present invention relates to apparatus and methods fordelivering biocidal-effective amounts of a gas such as chlorine dioxide.The apparatus and methods of the present invention achieve delivery of adesired amount of gas, at a desired rate, over a desired time period.This is accomplished by disposing suitable reactants in a defined andconfined volume such that upon initiation, the reactants, initiatingagent, products, and by-products are held within a desired concentrationrange. The amount, rate and duration of delivery can be manipulated by,e.g., choice of sachet layers, sachet volume, reactant amount, reactantratio, envelope layers, and envelope volume. Such manipulations can beexercised by the artisan using only routine experimentation in view ofthe teachings disclosed herein together with knowledge in the art.

[0049]FIGS. 1A and 1B are a perspective view and a cross-sectional sideview, respectively, of an embodiment of an apparatus 10 constructed inaccordance with the present invention. In general overview, apparatus 10includes an envelope 20, a sachet 30 disposed within the envelope 10,and reactant 40 disposed within sachet 30 that generates a gas in thepresence of an initiating agent, e.g., water. Envelope 20 allows contactof the initiating agent with sachet 30 and release of the gas fromenvelope 20.

[0050] Apparatus 10 is particularly useful for the rapid release of agas for wet applications e.g., delivery of 5 to 50 mg chlorine dioxidegas per liter of water in 5 to 15 minutes. The function of the envelopeis to control the influx of the initiating agent, while limiting thediffusion of the reactants from the sachet to the surrounding fluid, beit gaseous or liquid. The envelope also allows the gas to diffuse to thesurrounding fluid, be it gaseous or liquid. By limiting transmission ofthe initiating agent into the apparatus, and limiting and/or preventingdiffusion of the reactants out of the apparatus, the reactant remainsconcentrated and the pH of the reactive system is localized within theapparatus to optimize the conversion of reactant to gas. Additionally,intermediates and/or by-products of the reaction, e.g., water, also cancontribute to the efficiency and/or duration of the reaction by itsaffect on the equilibrium of the reactions.

[0051] The envelope preferably is constructed of a material that isdurable and stable. Preferably, it also is capable of fusing to a likematerial upon the application of heat for construction purposes, e.g.,so that two pieces of such material can be fused about its perimeter toform the envelope. The envelope can be constructed of various materials,including polymeric material, such as perforated films, membranes andselective transmission films.

[0052] Preferably, the envelope is constructed of envelope layers havinga water vapor transmission rate (WVTR) between about 50 g/m²/24 hrs andabout 1,000 g/m²/24 hrs, more preferably, between about 200 g/m²/24 hrsand about 800 g/m²/24 hrs, and most preferably between about 400 g/m²/24hrs and about 700 g/m²/24 hrs. The measurement of water vaportransmission rate is routine and well known in the art. Also, theenvelope preferably is hydrophobic.

[0053] Perforated films suitable for the construction of the envelope inaccordance with the present invention include, but are not limited to,polymeric material, e.g., Cryovac® perforated films available fromSealed Air Corporation (Duncan, S.C.). One such film is a hydrophobicpolypropylene copolymer film sold under the designation SM700 by SealedAir Corporation and has 330 holes per square inch having a diameter of0.4 mm, a 6.4% perforated area and a water vapor transmission rate of700 g/m²/24 hrs. Another suitable film is a hydrophobic polypropylenecopolymer film sold under the designation SM60 by Sealed Air Corporationand has 8 holes per square inch having a diameter of 0.4 mm, a 0.2%perforated area and a water vapor transmission rate of 65 g/m²/24 hrs.The artisan can readily identify suitable equivalents of any of theforegoing by exercising routine experimentation.

[0054] Selective transmission films are films that are neitherperforated nor porous, but instead transfer gases through the polymerstructure of the film. Selective transmission films are multilayeredpolyolefin materials, where the layers are chosen and coextruded forcontrolled transmission of gases such as carbon dioxide and oxygen.Selective transmission films are preferred in dry applications becauseit allows the gas to diffuse out of the envelope, while retaining theinitiating agent once released from the frangible pouch. Moreover, theselective transmission film increases the stability of the apparatusprior to its use because it does not easily allow ambient water todiffuse into the apparatus, which could prematurely initiate thereactants.

[0055] Generally, a film that has a high carbon dioxide transmissionrate is preferred. While not wishing to be bound to any theory, it isthought that the carbon dioxide transmission rate approximates thechlorine dioxide transmission rate because chlorine dioxide and carbondioxide are about the same size. Preferably, the selective transmissivefilm has a selective gas transmission rate of between about 500 cc/m²/24hrs and about 30,000 cc/m²/24 hrs for CO₂ and between about 1,000cc/m²/24 hrs and about 10,000 cc/m²/24 hrs for O₂. More preferably, theenvelope is constructed of a material having a selective gastransmission rate of between about 1,000 cc/m²/24 hrs and about 25,000cc/m²/24 hrs for CO₂ and between about 2,000 cc/m²/24 hrs and about10,000 cc/m²/24 hrs for O₂. Most preferably, the envelope is constructedof a material having a selective gas transmission rate of between about5,000 cc/m²/24 hrs and about 25,000 cc/m²/24 hrs for CO₂ and betweenabout 3,000 cc/m²/24 hrs and about 10,000 cc/m²/24 hrs for O₂.Measurement of selective gas transmission rate is routine and well knownin the art. One suitable selective transmission film is a multilayeredpolymer film having a carbon dioxide transmission rate of 21,000cc/m²/24 hrs and an oxygen transmission rate of 7,000 cc/m²/24 hrs soldunder the trade designation PD-961 Cryovact selective transmission filmfrom Sealed Air Corporation (Duncan, S.C.).

[0056]FIG. 6 is a graph depicting gas concentration versus timecomparing various apparatus fabricated with and without an envelope. Thesquare-shaped data points correspond to an apparatus with an envelopeconstructed with perforated film sold under the trade designation SM60by Sealed Air Corporation (Duncan, S.C.). As described above, thisperforated film has 8 holes per square inch having a diameter of 0.4 mm,a 0.2% perforated area and a water vapor transmission rate of 65 g/m²/24hrs. The diamond-shaped data points correspond to an apparatus withoutan envelope. Both apparatus contain 50 mg sodium chlorite and 200 mgcitric acid. Both include a sachet constructed from an extrudedpolypropylene hydrophilic membrane having a 0.65 micron pore size, soldunder the trade designation JOTD obtained from Millipore (Bedford,Mass.). For both apparatus, the sachet volume was about 5.5 times thevolume of the reactants. Both apparatus were each immersed in 1 liter ofwater and the chlorine dioxide concentration measured every 5 minutesfor an hour.

[0057]FIG. 6 demonstrates that the inclusion of an envelope increasesthe reaction efficiency, and consequently, the amount of gas deliveredfor the same amount and ratio of reactant is greatly increased. In FIG.6, the apparatus delivers about 12.5 mg of chlorine dioxide gas comparedto the approximately 4 mg delivered by the apparatus without anenvelope. Thus, the apparatus with the envelope delivered more than 3times the chlorine dioxide delivered by the apparatus without it, bothapparatus having the same amount and ratio of reactant and the samesachet layer. Moreover, FIG. 6 demonstrates the envelope increased thelength of time in which gas was generated by about 25 minutes. Ofcourse, there may be instances where having only a sachet, i.e., noenvelope, may be advantageous. For example, where the performance of theapparatus without an envelope is sufficient, having only a sachet may bepreferred because production is simplified, as the step of constructingthe envelope is eliminated, and also because material costs may bedecreased by eliminating the need to provide envelope layers toconstruct the envelope.

[0058]FIG. 7 is a graph depicting gas concentration versus timecomparing exemplary apparatus fabricated with envelope materials havingdifferent water vapor transmission rates. The triangular-shaped datapoints correspond to an apparatus without an envelope. The square-shapeddata points correspond to an apparatus with an envelope constructed fromperforated film sold under the trade designation SM700 by Sealed AirCorporation (Duncan, S.C.) having 330 holes per square inch having adiameter of 0.4 mm, a 6.4% perforated area and a water vaportransmission rate (WVTR) of 700 g/m²/24 hrs. The diamond-shaped datapoints correspond to an apparatus with an envelope constructed withperforated film sold under the designation SM60 by Sealed AirCorporation (Duncan, S.C.) having 8 holes per square inch having adiameter of 0.4 mm, a 0.2% perforated area and a water vaportransmission rate of 65 g/m²/24 hrs. All three apparatus contain thesame reactant and amount and ratio of reactant as used for the apparatusin FIG. 6. For all three apparatus, the sachet volume was about 5.5times the volume of the reactants. The reactants were enclosed sachetsconstructed from 0.65 micron pore size, hydrophobic, non-wovenpolypropylene material sold under the trade designation ANO6 byMillipore (Bedford, Mass.). These apparatus also were each immersed in 1liter of water and the chlorine dioxide concentration measured every 5minutes for an hour.

[0059]FIG. 7 demonstrates the effect of the water vapor transmissionrate of the envelope on the rate and efficiency of the reaction. In FIG.7, the apparatus having no envelope has a greater rate of reaction forabout the first 15 minutes, but is less efficient than the apparatuswith envelopes, delivering only about 12 mg of chlorine dioxide. Theapparatus having envelopes exhibit greater efficiency and a longer rateof gas generation, which is proportional to the water vapor transmissionrate (WVTR). The envelope with a water vapor transmission rate of 65g/m²/24 hrs has the greatest efficiency at about 55 minutes, generatingabout 22 mg of chlorine dioxide at a rate of about 5.5 mg of chlorinedioxide every 15 minutes. The envelope with a transmission rate of 700g/m²/24 hrs generates about 18 mg of chlorine dioxide in about 55minutes at a rate of about 4.5 mg of chlorine dioxide every 15 minutes.Thus, for applications where it is desired to increase efficiency and togenerate gas over an increased period of time, an envelope with a lowvapor transmission rate is preferred. As mentioned above, however, theremay be may be applications where having a less efficient apparatus maybe advantageous, e.g., decreased material and/or production costs.

[0060] By increasing or decreasing the water vapor transmission rate,the practitioner can control the rate and efficiency of the reaction tosuit the application. For example, it has been found that an apparatushaving a hydrophobic polypropylene envelope with a pore size of 0.1micron, a 0.65 micron pore size hydrophilic polypropylene sachet, andreactants that include 500 mg sodium chlorite and 2000 mg citric acid,will generate 3.5 mg/L chlorine dioxide gas per hour for at least 30hours.

[0061] It has been discovered that the use of a sachet can be used tolimit the diffusion of the initiating agent into the sachet, and limitthe diffusion of reactant and reactant by-products out of the sachet. Asa consequence, the reactants are and remain concentrated within thesachet and the pH remains localized increasing the efficiency of thereaction. Various attributes of the sachet, such as pore size, bubblepoint, and hydrophobic and/or hydrophilic nature of the sachet membrane,can be manipulated to control the affect of the sachet on the reactionas is described below.

[0062] The sachet preferably is constructed of a material that isdurable and stable. Preferably, it also is capable of fusing to a likematerial upon the application of heat for construction purposes, e.g.,so that two pieces of such material can be fused about its perimeter toform the sachet.

[0063] Envelopes and sachets of the present invention can be sealedabout their perimeter by any known method, such as heat sealing,ultrasonic sealing, radio frequency sealing, and sealing with adhesives.A preferred method of forming envelopes and sachets is to use an impulsesealer, which delivers a rapid and discreet thermal pulse to the layers.One impulse sealer suitable for use in accordance with the presentinvention is the 16″ TISH400 Impulse Sealer available from TEW ElectricHeating Equipment Corporation (Taiwan).

[0064] The sachet can be constructed of various materials, includingpolymeric material or coated papers. It can be constructed from wovenmaterial, non-woven membrane, extruded membrane, or any other materialwith a controlled pore distribution having a mean pore size betweenabout 0.01 μand about 50 μm.

[0065] A woven material is any material woven from cotton, metal,polymer threads, metal threads or the like into a cloth or mesh.Extruded membranes, which include cast membranes, are preferred, andinclude 0.65 micron pore size, hydrophilic polypropylene sachet soldunder the trade designation MPLC from Millipore (Bedford, Mass.), 0.65micron pore size, extruded hydrophobic polypropylene material sold underthe trade designation DHOP by Millipore (Bedford, Mass.). Also preferredis the cast membrane 3 micron pore Nylon 66 material sold under thetrade designation BIODYNE A by Pall (Port Washington, N.Y.). Non-wovenmembranes are membranes formed from materials such as cellulose orpolymers.

[0066] Non-wovens membranes can be formed, e.g., by suspending themembrane material, e.g, cellulose fibers, in a liquid over a porous weband then draining the liquid to form a membrane. Non-woven membranestypically have a relatively narrow and consistent pore size distributionas compared to woven materials. Consequently, the non-woven sachetgenerally allows less initiating agent into the sachet than the wovensachet having the same pore size because, generally the pore sizedistribution is narrower. A non-woven membrane suitable for use inaccordance with the present invention is the 0.65 micron pore size,hydrophobic, non-woven polypropylene material sold under the tradedesignation ANO6 by Millipore (Bedford, Mass.).

[0067] In a preferred embodiment the sachet is constructed from amembrane having a pore size between about 0.01 μm and about 50 μm. Morepreferably, the pore size is between about 0.05 μm and about 40 μm, andmost preferably, the pore size is between about 0.10 ρm and 30 μm. Thepore size of the sachet is measured by bubble point. Bubble point is ameasurement well known in the art which approximates pore size from ameasurement of the pressure necessary to drive a bubble of water throughthe sachet. Pore size affects the rate at which water and ions candiffuse through the sachet in both directions. A pore size preferably ischosen that allows entry of initiating agent into the sachet and, at thesame time, retains the reactants within the sachet at a highconcentration so that the reaction rate is increased and a highefficiency maintained. The artisan can readily identify suitableequivalents of any of the foregoing by exercising routineexperimentation.

[0068] In certain preferred embodiments, the material used to constructthe sachet preferably has a bubble point between about 3 psi and about100 psi, more preferably between about 5 psi and about 80 psi, and mostpreferably between about 10 psi and about 70 psi. As mentionedpreviously, the measurement of bubble point is routine and well known inthe art and typically is supplied by suppliers of membranes, films,etc., however, the practitioner can readily make measurement.

[0069] Additionally, the sachet can be constructed from material that ishydrophobic and/or hydrophilic. It can also comprise a material havingone or more hydrophilic zones and one or more hydrophobic zones. Thesezones can be created, e.g., by printing a functional chemical group orpolymer onto a surface of the sachet that is hydrophilic or hydrophobicor charged to create one or more hydrophilic or hydrophobic or chargedzones. For example, a sulfonic acid group can be disposed on the surfaceof the polypropylene membrane, creating zones that are both hydrophilicand negatively charged (R—SO₂ ⁻). The membrane can then washed with adilute acid such that the ion exchange groups (R—SO₂ ⁻) bind the H⁺ions. These H⁺ ions can later be released to supply H⁺ ions to acidactivate reactant, e.g., chlorite, as a replacement or supplement toacid reactant.

[0070] When the sachet is constructed of hydrophobic material, thehydrophobic material preferably has a flow time between about 10 sec/500ml and about 3,500 sec/500 ml for 100% IPA at 14.2 psi. More preferably,the material has a flow time between about 60 sec/500 ml and about 2,500sec/500 ml for 100% IPA at 14.2 psi, and most preferably, the materialhas a flow time between about 120 sec/500 ml and about 1,500 sec/500 mlfor 100% IPA at 14.2 psi.

[0071] When the sachet is constructed of hydrophilic material asdescribed above the hydrophilic material preferably has a flow timebetween about 5 sec/500 ml and about 800 sec/500 ml for 100% IPA at 14.2psi. More preferably, the material has a flow time between about 20sec/500 ml and about 400 sec/500 ml for 100% IPA at 14.2 psi, and mostpreferably, the material has a flow time between about 50 sec/500 ml andabout 300 sec/500 ml for 100% IPA at 14.2 psi. Measurement of flow timeis routine and well known in the art.

[0072] Yet another alternative embodiment uses a material to constructthe sachet that has a first surface that is hydrophilic and a secondsurface that is hydrophobic. For example, a sachet can be constructedfrom such a material such that the hydrophilic surface is on the outsideof the sachet and the hydrophobic surface is on the inside of thesachet. The exterior, hydrophilic surface aids the initiation of thereaction since water will readily wet a hydrophilic surface and enterthe sachet. However, once inside the sachet, the hydrophobic, interiorsurface limits water passage out of the sachet. This keeps the reactantsconcentrated within the sachet while allowing the gas to escape thusexploiting the advantages of the discoveries disclosed herein. One suchmaterial suitable for use in the present invention is a non-wovenmembrane 0.65 micron pore size diameter formed from a hydrophobicmaterial, such as polypropylene, that has been chemically functionalizedwith amines and carboxyl groups to produce a charge, hydrophilicsurface.

[0073] The ratio of sachet volume to reactant volume also can bemanipulated to control the concentration of the reactants,intermediates, by-products, etc. within the sachet. As discussedpreviously, increasing the concentration of reactants generallyincreases reaction efficiency. Preferably the sachet volume is less thanabout 20 times the volume of reactant, more preferably less than about10 times the volume of the reactant. Most preferably, it is less than 6times the volume of the reactants. Smaller volumes are preferred incertain applications because when the ratio of sachet volume to reactantvolume is small, water produced in the reaction increases the pressureinside the sachet reducing the rate at which water can diffuse into thesachet, the water to reactant ratio remains constant and thus the rateof reaction remains constant. Preferably the volume of the envelope isfrom about 2 to about 6 times the volume of the sachet.

[0074]FIG. 8 is a graph depicting gas concentration versus timecomparing exemplary apparatus fabricated with and without a sachet.Specifically, FIG. 8 depicts gas concentration versus time comparingdelivery of chlorine gas from reactant within a sachet versus reactantadded directly to water, i.e., with neither sachet nor envelope. Thetriangular-shaped data points indicate the rate of delivery of chlorinedioxide over time in 1 liter of water from a sachet material constructedfrom a 0.65 micron pore size, hydrophilic polypropylene membrane soldunder the trade designation MPLC by Millipore (Bedford, Conn.). Thesachet contained 200 mg citric acid and 50 mg of sodium chlorite. Thesachet volume was about 5.5 times the volume of the reactants. Thesachet was enclosed in an envelope constructed from perforated film soldunder the trade designation SM700 by Sealed Air Corporation having 330holes per square inch having a diameter of 0.4 mm, a 6.4% perforatedarea and a water vapor transmission rate of 700 g/m²/24 hrs. Thediamond-shaped data points indicate the rate of delivery of chlorinedioxide over time when the same reactants in the same amounts were addedto 1 liter of water directly, i.e., with neither sachet nor envelope.The apparatus with the sachet delivered more than 10 times the chlorinedioxide than when the reactants were added directly to the water. As canbe seen from FIG. 8, the sachet increases the efficiency of thereaction.

[0075]FIG. 9 is a graph depicting gas concentration versus timecomparing an exemplary apparatus fabricated with extruded and non-wovensachets. The diamond-shaped data points indicate delivery of chorinedioxide over time for the apparatus with a sachet constructed from 0.65micron pore size, hydrophobic, non-woven polypropylene material soldunder the trade designation ANO6 by Millipore (Bedford, Mass.). Thesquare-shaped data points indicate delivery of chorine dioxide over timefor the apparatus with a sachet constructed from 0.65 micron pore size,extruded hydrophobic polypropylene material sold under the tradedesignation DHOP by Millipore (Bedford, Mass.). Both sachets contained200 mg citric acid and 50 mg of sodium chlorite and the sachet volumewas about 5.5 times the volume of the reactants. Neither apparatusincluded an envelope. The apparatus were each immersed in 1 liter ofwater and the chlorine dioxide gas concentration measured every fiveminutes for an hour.

[0076] As shown in FIG. 9, both apparatus deliver chlorine dioxide atapproximately the same rate for about the first 20 minutes. However, asthe reactants become increasingly dilute in the extruded sachet relativeto the non-woven sachet, the rate of the chlorine dioxide releasediminishes. The efficiency of the reaction in the apparatus with thenon-woven sachet is greater than that with the extruded sachet. Theapparatus with the non-woven sachet also continue to generate chlorinedioxide gas at a rate of about 2 mg every 5 minutes for about 15 minuteslonger than the apparatus with the extruded sachet. As mentioned above,non-woven sachets generally have a relatively narrow pore sizedistribution, and without wishing to be bound to any theory, it isthought that this accounts for the greater efficiency and longer periodof gas generation. Thus, FIG. 9 provides a non-limiting illustration ofhow sachet material choice, and thus reactant concentration, can beexploited to sustain the rate of gas release and increase theefficiency.

[0077]FIG. 10 is a graph depicting gas generation versus time comparingexemplary apparatus fabricated with sachets made of materials havinghydrophobic and hydrophilic surfaces. The triangular-shaped data pointscorrespond to an apparatus with a sachet constructed from 0.65 micronpore size, hydrophilic polypropylene sachet sold under the tradedesignation MPLC from Millipore (Bedford, Mass.). The diamond-shapeddata points correspond to an apparatus with a sachet constructed from0.65 micron pore size, extruded hydrophobic polypropylene material soldunder the trade designation DHOP by Millipore (Bedford, Mass.). Thesquare-shaped data points correspond to adding the reactant directly tothe water. The reactant was 200 mg citric acid and 50 mg of sodiumchlorite and the sachet volume was about 5.5 times the volume of thereactants. Neither sachet was enclosed in an envelope. The apparatus andthe reactant were each immersed in 1 liter of water and the chlorinedioxide gas concentration was measured every 5 minutes for an hour.

[0078]FIG. 10 demonstrates that apparatus having a hydrophobic sachetresults in a more efficient reaction that generates gas over a longerperiod of time than a sachet. In FIG. 10, the apparatus with thehydrophobic sachet generated chlorine dioxide for about 30 minutes atabout 2 mg every 5 minutes. In contrast, the apparatus with thehydrophilic sachet generated chlorine dioxide only for about 10 minutesat about 2 mg every 5 minutes. As disclosed above in connection withFIG. 6, adding an envelope to either sachet will have the effect ofincreasing the efficiency of the reaction as well as increasing thelength of time in which gas is generated.

[0079] The reactant preferably comprises an aqueous soluble acid and areactant that upon acid activation generates a gas. For example, for thegeneration of chlorine dioxide, preferably the reactant comprises anaqueous soluble acid and an aqueous soluble chlorite. For the generationof sulfur dioxide, preferably the reactant comprises an aqueous solubleacid and an aqueous soluble sulfite. Other examples of gas generatingreactions are disclosed above.

[0080] Any acid can be used as a reactant. However, weak acids arepreferred, as they typically are safer to handle, produce lessundesirable by-products, and are less reactive. Also, multifunctionalacids are preferred. Multifunctional acids are acids that have more thanone reactive site. For example, the difunctional acid, citric acid, ispreferred. Preferably, the aqueous soluble acid is selected from thegroup consisting of phosphoric acid, fumaric acid, glycolic acid, aceticacid, ascorbic acid, oxalic acid, maleic acid, lactic acid, tartaricacid, citric acid and mixtures thereof. More preferably, the aqueoussoluble acid is selected from the group consisting of ascorbic acid,oxalic acid, maleic acid, lactic acid, tartaric acid, citric acid andmixtures thereof. Most preferably, the aqueous soluble acid is ascorbicacid, oxalic acid, citric acid and mixtures thereof.

[0081] For applications involving the generation of chlorine dioxide,preferably the aqueous soluble chlorite is selected from a groupconsisting of sodium chlorite and potassium chlorite and mixturesthereof. Preferably sodium chlorite is used.

[0082] Preferably, the weight ratio of the aqueous soluble chlorite tothe aqueous soluble acid is between about 1:2 to about 1:6, preferablyfrom about 1:2.5 to about 1:5, most preferably from about 1:3 to about1:4.5. Preferably, a pH between about 1.5 to 5.5, more preferably a pHof about 2, is maintained by using an excess of acid. Because thereactants are concentrated within the sachet, less acid is needed todrive the reaction to completion and the pH remains low because the acidis concentrated. Furthermore, chlorite is consumed by acid and thereforethe presence of chlorite is minimized.

[0083]FIG. 11 is a graph depicting gas concentration versus timecomparing apparatus fabricated with two different reactant ratios. Thesquare-shaped data points correspond to an apparatus with a 1:4 ratio ofcitric acid to sodium chlorite (50 mg sodium chlorite and 200 mg ofcitric acid). The diamond-shaped data points correspond to an apparatuswith a 1:1 ratio of citric acid to sodium chlorite (50 mg sodiumchlorite and 50 mg citric acid). Both apparatus included a sachetconstructed from 0.65 micron pore size, hydrophilic, polypropylenesachet sold under the trade designation MPLC from Millipore (Bedford,Mass.). The sachet volume was about 5.5 times the volume of thereactants. Both sachets were enclosed in an envelope constructed fromperforated film sold under the trade designation SM700 by Sealed AirCorporation having 330 holes per square inch having a diameter of 0.4mm, a 6.4% perforated area and a water vapor transmission rate of 700g/m²/24 hrs. These apparatus were immersed in 1 liter of water and thechlorine dioxide gas concentration measured every 5 minutes for an hour.

[0084]FIG. 11 demonstrates that increasing the amount of citric acidrelative to the amount of sodium chlorite increases the efficiency ofthe reaction, in part because the excess of acid drives the reaction tocompletion. The relationship of efficiency to reactant ratio is fairlypredictable when the ratio of sodium chlorite to citric acid is betweenabout 1:1 and about 1:6. Above about 1:6, there is little change in theefficiency of the reaction.

[0085] Ambient temperature also can affect the efficiency of thereaction. Generally, the hotter the temperature of the ambient fluid,e.g., water or air, the more efficient the generation of gas. Generally,however between the ranges of 10° C. and 40° C., the efficiency improvesas the temperature increases. The data used to generate FIGS. 6 through11 and the Examples are from apparatus tested at from about 23° C. toabout 25° C. The sachet also can include various other ingredients thatwill be obvious to one skilled in the art, such as drying agents,stabilizers, and buffers to control the pH.

[0086] It also should be understood that the apparatus and methods ofthe present invention also are readily applicable to the delivery ofmore than one gas at one time. For example, the reactant can includeboth a chlorite and at sulfite for the delivery of both chlorine dioxideand sulfur dioxide.

[0087]FIGS. 2A and 2B are a perspective view and a cross-sectional sideview, respectively, of another embodiment of an apparatus 110constructed in accordance with the present invention. In generaloverview, apparatus 110 includes envelope 120 and two sachets 132, 134disposed within the envelope 120. Sachets 132, 134 contain reactant 142,144, respectively.

[0088] The envelope and sachet can be constructed from any of thematerial discussed in references to FIGS. 1A and 1B. Preferably, theenvelope is a hydrophobic perforated film, such as the polypropylenecopolymer film sold under the designation SM700 by Sealed AirCorporation (Duncan, S.C.) having 330 holes per square inch having adiameter of 0.4 mm, a 6.4% perforated area and a water vaportransmission rate of 700 g/m²/24 hr. The envelope can also beconstructed from 0.65 micron pore hydrophobic polypropylene membrane,such as that sold under the trade designation DHOP by Millipore(Bedford, Mass.)

[0089] Sachets 132, 134 can be constructed from hydrophobic membraneand/or hydrophilic membrane. Preferred materials for sachets 132, 134are described in connection with the embodiment of FIGS. 1A and 1B.Preferably, the sachets 132, 134 are constructed from a hydrophilicmaterial, e.g., 0.65 micron pore size hydrophilic polypropylenemembrane, such as that sold under the designation MPLC by Millipore(Bedford, Mass.), or extruded polypropylene hydrophilic membrane havinga 0.65 micron pore size, sold under the trade designation JOTD obtainedfrom Millipore (Bedford, Mass.).

[0090] Reactant 142, 144 preferably includes an aqueous soluble acid andan aqueous chlorite that upon acid activation generates a gas.Preferably, these components are not mixed, but instead are separatelycontained in sachets 132, 134. It is preferred to separately contain thechlorite and the acid because this minimizes the likelihood of prematureinitiation, e.g., during storage and shipment. Reactant 142, 144 can beliquid or solid, but is preferably solid.

[0091] In a preferred embodiment, the envelope 120 is hydrophobic andthe sachets 132, 134 are hydrophilic. This preferred embodiment isparticularly suitable for the delivery of gas in wet applications andhas a slower rate of gas delivery than apparatus 10 of FIGS. 1A and 1B.For example, this embodiment can be used to deliver gas at low ratesover long periods of time, e.g., 20 mg of gas per hour over a 24 hourperiod. This embodiment also is preferred for applications where a highefficiency and concentration of gas is desired and it is possible toallow the apparatus a period of time to complete delivery, e.g., 4 to 8hours.

[0092] Optionally, this embodiment could contain a second envelope (notshown) enclosing the first envelope 120. This second envelope might beuseful, for example, in further regulating the introduction of theinitiating agent through the envelope walls.

[0093]FIGS. 3A and 3B are a perspective view and a cross-sectional sideview, respectively, of an apparatus 210 constructed in accordance withthe present invention. Apparatus 210 includes first sachet 232, firstreactant 242 disposed within first sachet 232, second sachet 234, secondreactant 244 disposed within second sachet 234, third sachet 250disposed about first sachet 232 and second sachet 234, and envelope 220disposed about third sachet 250. Disposed within the envelope 220adjacent to the third sachet 250 is frangible pouch 260, and initiatingagent 264 disposed within frangible pouch 260.

[0094] Apparatus 210 is particularly useful for the delivery of gas in adry application because initiating agent 264 is contained within theapparatus 210. In this embodiment, first reactant 242 and secondreactant 244 generate a gas in the presence of initiating agent 264. Forthis to occur, frangible pouch 260 is ruptured, e.g., by exertingpressure on frangible pouch 260 so that initiating agent 264 isdelivered into first envelope 220. Third sachet 250 allows contact ofinitiating agent 264 with first sachet 232 and second sachet 242.

[0095] First sachet 232, second sachet 234, first reactant 242 andsecond reactant 244 are described above in reference to the embodimentsshown in FIGS. 1A, 1B, 2A and 2B. In a currently preferred embodiment,first sachet 232 and second sachet 234 are constructed from ahydrophilic material having a pore size between about 3 microns and 5microns. A suitable material is a 3 micron pore Nylon 66 material soldunder the trade designation BIODYNE A by Pall (Port Washington, N.Y.).

[0096] Third sachet 250 preferably is constructed using the materialsdescribed above in reference to the sachet material for the embodimentsdescribed for FIGS. 2A and 2B. The materials described above inreference to the embodiment described for FIGS. 1A and 1B can also beused. A suitable sachet layers is 0.65 micron pore hydrophobicpolypropylene membrane, Such as that sold under the trade designationDHOP by Millipore (Bedford, Mass.). The third sachet limits thediffusion of reactant out of the third sachet and thus, it keeps thereactant concentrated within the third sachet and the pH localized.Preferably, the third sachet volume is less than 4 times that of thefirst reactant and the second reactant combined, and most preferablyless than 2 times that of the first reactant and the second reactantcombined.

[0097] Preferably, envelope 220 is constructed from a selectivetransmission film. Selective transmission films are described above inconnection with FIGS. 1A and 1B. As discussed above, selectivetransmission films are preferred in dry applications because it allowsthe gas to diffuse out of the envelope, while retaining the initiatingagent once released from the frangible pouch. Moreover, the selectivetransmission film increases the stability of the apparatus prior to itsuse because it does not easily allow ambient water to diffuse into theapparatus, which could prematurely initiate the reactants. Furthermore,keeping the reactant, e.g, sodium chlorite and acid, separated into twosachets also can increase the stability of the apparatus because itretards initiation should initiating agent diffuse into the apparatusprior to rupturing the frangible pouch.

[0098] One suitable selective transmission film is a multilayeredpolymer film having a carbon dioxide transmission rate of 21,000cc/m²/24 hrs and an oxygen transmission rate of 7,000 cc/m²/24 hrs soldunder the trade designation PD-961 Cryovac® selective transmission filmfrom Sealed Air Corporation (Duncan, S.C.).

[0099] Frangible pouch 260 can be constructed of any material thatruptures when pressure is applied to the envelope thus releasing theinitiating agent inside it. Preferably, the frangible pouch isconstructed from a multi-layer plastic, e.g., polyolefin, envelopehaving a weak layer positioned near the sealing surface that will failunder pressure. Initiating agent 264 can be any agent that initiates agasgenerating reaction, e.g., water. Preferably the initiating agent iswater or an aqueous solution, but is not limited thereto.

[0100]FIGS. 4A and 4B are a perspective view and a cross-sectional sideview, respectively, of still yet another embodiment of an apparatus 310constructed in accordance with the present invention. In generaloverview, apparatus 310 includes sachet 370 and partition 380 disposedwithin sachet 370 defining first volume 382 and second volume 384 withinsachet 370. Also shown is first reactant 342 disposed within firstvolume 382 and second reactant 344 disposed within second volume 384. Inthis embodiment, first reactant 342 and second reactant 344 generate agas in the presence of an initiating agent, and envelope 370 allowsentry of an initiating agent into apparatus 310.

[0101] Preferably, sachet 370 is constructed using a hydrophobicmembrane to retard entry of the initiating agent into the apparatus.Preferably, partition 380 is constructed using hydrophilic membrane sothat the initiating agent, once within the apparatus, will migrate topartition 380. These hydrophobic and hydrophilic membranes are describedabove for the embodiments depicted in FIGS. 1A, 1B, 2A, and 2B.Similarly first reactant 342 and second reactant 344 are described abovefor the embodiments depicted in FIGS. 1A, 1B, 2A, and 2B. If, forexample, first reactant 342 consists of sodium chlorite and secondreactant 344 consists of citric acid, reaction begins when an initiatingagent reaches partition 380. In a preferred embodiment, sachet 370 isconstructed from 0.65 micron pore hydrophobic polypropylene membrane,such as that sold under the trade designation DHOP by Millipore(Bedford, Mass.), and partition 380 is constructed from 0.65 micron porehydrophilic polypropylene membrane, such as that sold under thedesignation MPLC by Millipore (Bedford, Mass.).

[0102] Optionally, the apparatus depicted in FIGS. 4A and 4B may furthercomprise an envelope (not shown) enclosing the sachet. This envelope canbe constructed from any of the envelope materials described above forthe embodiments depicted in FIGS. 1A, 1B, 2A and 2B. Preferably, theenvelope is a hydrophobic perforated film, such as the polypropylenecopolymer film sold under the designation SM700 by Sealed AirCorporation (Duncan, S.C.) having 330 holes per square inch having adiameter of 0.4 mm, a 6.4% perforated area and a water vaportransmission rate of 700 g/m²/24 hr.

[0103]FIGS. 5A and 5B are a perspective view and a cross-sectional sideview, respectively, of still yet another embodiment of an apparatus 410constructed in accordance with the present invention. In generaloverview, apparatus 410 includes sachet 430 and reactant 440 disposedwithin sachet 430 that generates a gas in the presence of an initiatingagent. Sachet 430 allows contact of the initiating agent with thereactant and release of the gas from the apparatus.

[0104] There may be instances where having only a sachet, i.e., noenvelope, may be preferred over embodiments that further includeenvelopes. For example, where the performance of the apparatus withoutan envelope is sufficient, this embodiment is preferred, becauseproduction is simplified as the step of constructing the envelope iseliminated, and also because material costs may be decreased byeliminating the need to provide envelope layers to construct theenvelope.

[0105] Sachet materials can be constructed from the materials describedabove for the embodiments depicted in FIGS. 1A, 1B, 2A, and 2B.Preferably, the sachet is constructed using hydrophobic membrane so thatthe sachet limits the amount of water entering the sachet. Similarly,reactant 440 is described above or the embodiments depicted in FIGS. 1A,1B, 2A, and 2B.

[0106]FIGS. 8, 9, and 10 depict concentration versus time for variousapparatus that include a sachet but do not include envelopes. Acurrently preferred embodiment is an apparatus where the sachet isconstructed from a 0.65 micron pore size, hydrophobic polypropylenemembrane sold under the trade designation DHOP by Millipore (Bedford,Mass.). The diamond-shaped data points in FIGS. 9 and 10 depict theperformance of an apparatus with a sachet and without an envelopeconstructed from this material.

[0107] In view of the collective teachings and guidance set forthherein, the practitioner can design, fabricate, test and use any numberof embodiments of the present invention. All that is required is anordinary level of skill in the art and some routine experimentation. Forexample, for a disinfection application, a practitioner initially shoulddetermine the volume to be disinfected using a gas-generating apparatusof the instant invention. Next, appreciating that the current standardfor cold sterilization/disinfection is 5 mg/L chlorine dioxide, thepractitioner should determine the quantity of chlorine dioxide that willbe required to disinfect the desired volume.

[0108] From the volume of chlorine dioxide gas required, the amount andratio of reactant necessary to generate this amount of chlorine dioxidecan be calculated. Of course, if a practitioner wishes to increase ordecrease the disinfecting concentration, then one can adjust thereactant quantities placed in a sachet. Representative data generatedwith varying ratios of reactants are depicted in FIG. 11, for example.Variations in amounts generally are proportional, e.g, doubling theamount of sodium chlorite will double the amount of chlorine dioxide gasgenerated, if all other elements of the apparatus remain the same. Ofcourse, the amount of gas generated can also be increased by envelopechoice as described in connection with FIGS. 6 and 7.

[0109] Also, the practitioner should determine the time course ofrelease of the disinfecting gas and choose sachet layers and envelopelayers accordingly. For example, if a rapid release is desired, thenreactants can be contained within a sachet fabricated from hydrophilicmaterial; if a less rapid release is desired, then reactants can becontained in a hydrophobic material. Representative data generated withhydrophobic and hydrophilic sachet material are depicted in FIG. 10.Representative data generated with reactants housed in variousembodiments of sachets and envelopes as taught by the present inventionare depicted in FIGS. 6 through 11. The skilled artisan will appreciatethat intermediate rates of release can be accomplished by mixing andmatching different sachet layers and different envelope layers. Onlyroutine experimentation is required.

[0110] Another aspect of the present invention features a method offorming an apparatus for delivery of a gas. This method includes thesteps of: (a) providing a multi-layer structure comprising a reactantlayer centrally disposed between two sachet layers, and two envelopelayers disposed adjacent to the two sachet layers such that the twosachet layers are centrally disposed between the two envelope layers;and (b) stamping the multi-layer structure such that the two envelopelayers form an envelope defined about its perimeter by the stamp, andthe two sachet layers form a sachet defined about its perimeter by thestamp.

[0111] This method has many variations and embodiments. For example, asecond reactant layer disposed between an additional two sachet layerscan be included between the two envelope layers prior to step (a), sothat upon stamping, the apparatus includes two sachets, each with itsown reactant layer inside. Another variant adds the following steps tothe method described above: (c) providing an initiating agent in afrangible pouch and a second two envelope layers, (d) stamping thesecond two envelope layers to form a second envelope defined about itsperimeter by the stamp, such that the frangible pouch and the envelopeformed in step (b) are disposed within the second envelope.

[0112] Stamping includes any method of forming an envelope from theenvelope layers and a sachet from the sachet layers, e.g., sealing theperimeter with a glue or other sealant, impulse sealing and heatsealing.

[0113] This method is advantageous because it allows the apparatus ofthe present invention to be manufactured quickly and inexpensivelyrelative to assembling and forming each individual sachet and envelopeseparately.

[0114] In another aspect, the above method can be modified to constructan apparatus without an envelope. For example, the method can includesthe steps of: (a) providing a multi-layer structure comprising areactant layer centrally disposed between two sachet layers; and (b)stamping the multi-layer structure such that the two sachet layers forma sachet defined about its perimeter by the stamp.

[0115] Yet another aspect of the present invention features a method ofdelivering gas. This method includes the steps of: (a) providing anapparatus for delivery of a gas comprising an envelope, a sachetdisposed within the envelope, and a reactant disposed within the sachetthat generates a gas in the presence of an initiating agent, wherein theenvelope allows release of the gas from the envelope; and (b) disposingthe apparatus in an environment that comprises an initiating agent.

[0116] This method has many variations and embodiments. For example, theenvironment can be liquid and the initiating agent can be water or theenvironment can be gaseous and the initiating agent can be water vapor.Preferably, the water vapor is that naturally diffused in the gaseousenvironment, e.g., atmospheric water diffused in air at ambienttemperature.

[0117] In another aspect, the above method can be modified to includesthe steps of: (a) providing an apparatus for delivery of a gascomprising a sachet and a reactant disposed within the sachet thatgenerates a gas in the presence of an initiating agent; and (b)disposing the apparatus in an environment that comprises an initiatingagent.

[0118] Optionally, to further increase stability of any of the apparatusof the present invention during storage and shipment, any desiccant,such as silica gel or molecular sieves, can be used to scavengeinitiating agent prior to use ol the apparatus.

EXAMPLE 1

[0119] An Apparatus in Accordance with the Present Invention

[0120] A membrane sachet was constructed by impulse sealing theperimeter of two 3 cm×3 cm sheets of 0.65 micron pore hydrophilicpolypropylene membrane sold under the trade designation MPLC obtainedfrom Millipore (Bedford, Mass.). The sheets were impulse sealed a 16″TISH400 Impulse Sealer available from TEW Electric Heating EquipmentCorporation (Taiwan). This sachet was filled with 50 mg of sodiumchlorite and 200 mg citric acid. The sachet was then placed into anenvelope formed by impulse sealing the perimeter of a 4 cm×6 cmperforated film. The perforated film used was a SM700 Cryovac®perforated film from Sealed Air Corporation (Duncan, S.C.). Thisassembly was then placed in a 1 liter plastic bag filled with water for15 minutes. The chlorine dioxide concentration in the water was measuredusing a Beckman DU-520 UV-Vis Spectrophotometer set at a wavelength of360λ at about 6 mg/L.

Comparative Example 2

[0121] Direct Addition of Reactant to Water

[0122] 50 mg of sodium chlorite and 200 mg citric acid were added to 1liter of water. The solution was allowed to sit for 15 minutes. Thechlorine dioxide concentration in the water was measured using a BeckmanDU-520 UV-Vis Spectrophotometer set at a wavelength of 360λ at about 0.5mg/L. FIGS. 8 and 10 depict gas generation over time for adding the sameamount and ratio of reactants to water.

EXAMPLE 3

[0123] An Apparatus without an Envelope

[0124] An apparatus was constructed as described in Example 1, exceptthat the envelope was not included. This assembly was then placed in a 1liter plastic bag filled with water for 15 minutes. The chlorine dioxideconcentration in the water was measured using a Beckman DU-520 UV-VisSpectrophotometer set at a wavelength of 360λ at about 5.5 mg/L. Such anapparatus and exemplary use of the same are depicted in FIG. 10.

EXAMPLE 4

[0125] An Apparatus Having Two Sachets

[0126] Two sachets were constructed by impulse sealing the perimeter offour 3 cm×3 cm sheets of 0.65 micron pore hydrophilic polypropylenemembrane sold under the trade designation MPLC obtained from Millipore(Bedford, Mass.). The first sachet was filled with 400 mg of sodiumchlorite and the second sachet was filled with 1200 mg citric acid. Bothsachets were then enclosed in an envelope formed by impulse sealing theperimeter of a 4 cm×6 cm SM700 film obtained from Sealed Air Corporationhaving 330 holes per square inch having a diameter of 0.4 mm, a 6.4%perforated area and a water vapor transmission rate of 700 g/m²/24 hr.This apparatus was then placed in a 1 liter plastic bag filled withwater and let stand for 180 minutes. The chlorine dioxide concentrationwas measured using a Beckman DU-520 UV-Vis Spectrophotometer set at awavelength of 360λ 100 mg/L.

EXAMPLE 5

[0127] An Apparatus Having Three Sachets and a Frangible PouchContaining an Initiating Agent

[0128] Two sachets were constructed in accordance with Example 4 exceptthat the sachets were constructed from 3 micron pore nylon 66 materialsold under the trade designation BIODYNE A from Pall (Port Washington,N.Y.). The first sachet was filled with 500 mg of sodium chlorite andthe second sachet was filled with 2000 mg citric acid. Both sachets werethen enclosed in a third sachet formed by impulse sealing the perimeterof a 5 cm×7 cm 0.65 micron pore, hydrophobic polypropylene membrane soldunder the trade designation DHOP by Millipore (Bedford, Mass.). Afrangible pouch was constructed and filled with 5 ml of water. Thefrangible pouch and the third sachet (containing the first and secondsachets and reactant) were then enclosed in an envelope formed byimpulse sealing the perimeter of a 7 cm×9 cm multilayered polymer filmhaving a carbon dioxide transmission rate of 7,000 cc/m²/24 hrs and anoxygen transmission rate of 21,000 cc/m²/24 hrs sold under the tradedesignation PD-961 Cryovac® selective transmission film from Sealed AirCorporation (Duncan, S.C.). This apparatus was then placed in a 1 literplastic bag filled with water and let stand for 180 minutes. Thechlorine dioxide concentration in the water was measured using a BeckmanDU-520 UV-Vis Spectrophotometer set at 360λ at 100 mg/L.

EXAMPLE 6

[0129] An Apparatus Having an Envelope and a Bridge

[0130] A two-compartment membrane sachet was constructed by impulsesealing the perimeter of a 3 cm×3 cm sheets of 0.65 micron porehydrophilic polypropylene membrane, sold under the trade designationMPLC obtained from Millipore (Bedford, Mass.), between two 3 cm×3 cmsheets of 0.65 micron pore hydrophobic polypropylene membrane sold underthe trade designation DHOP by Millipore (Bedford, Mass.). Thus wasformed a two compartment sachet having hydrophilic membrane on its outerwalls and a divider of hydrophobic membrane for separating the reactantin each compartment. The first compartment of the sachet was filled with50 mg of sodium chlorite and the second compartment was filled with 200mg citric acid. This multi-compartment sachet was then placed into anenvelope formed by heat-sealing the perimeter of a 4 cm×6 cm perforatedfilm. The perforated film used was a SM700 Cryovac® perforated film fromSealed Air Corporation (Duncan, S.C.). This assembly was then placed ina 1 liter plastic bag filled with water for 15 minutes. The chlorinedioxide concentration in the water was measured using a Beckman DU-520UV-Vis Spectrophotometer set at 360λ wavelength at about 8 mg/L

EXAMPLE 7

[0131] An Apparatus for Generating Carbon Dioxide

[0132] A sachet was constructed by impulse sealing the perimeter of two3 cm×3 cm sheets of 0.65 micron pore hydrophilic polypropylene membrane,sold under the trade designation MPLC obtained from Millipore (Bedford,Mass.). This sachet was filled with 50 mg of calcium carbonate and 100mg citric acid. The sachet was then placed into an envelope formed byimpulse sealing the perimeter of a 4 cm×6 cm perforated film. Theperforated film used was a SM700 Cryovac® perforated film from SealedAir Corporation (Duncan, S.C.). This assembly was then placed in a 1liter plastic bag filled with water for 15 minutes. The carbon dioxideconcentration in the water was measured using analyzed by ionchromatography at about 50 mg/L.

EXAMPLE 8

[0133] An Apparatus for Long-Term Release

[0134] A sachet was constructed by impulse sealing the perimeter of two4 cm×6 cm sheets of 0.65 micron pore hydrophilic polypropylene membrane,sold under the trade designation MPLC obtained from Millipore (Bedford,Mass.). This sachet was filled with 500 mg of sodium chlorite and 2000mg citric acid. The sachet was then placed into an envelope formed byimpulse sealing the perimeter of a 4 cm×6 cm perforated film. Theperforated film used was 0.1 micron pore hydrophobic polypropylenemembrane sold under the trade designation DHOP by Millipore (Bedford,Mass.). This apparatus was then placed in a 2 liter plastic bag filledwith water. The chlorine dioxide concentration was measured every hourusing a Beckman DU-520 UV-Vis Spectrophotometer set at a wavelength of360λ. The apparatus generated about 3.5 mg per hour for 30 hours.

[0135] Although generally the preferred embodiments of the inventionhave been shown and described, numerous variations and alternativeembodiments will occur to those skilled in the art. Accordingly, it isintended that the invention be limited only in terms of the appendedclaims as the invention can be embodied in other specific forms.

What is claimed is:
 1. An apparatus for delivery of a gas comprising: anenvelope; a sachet disposed within the envelope; and a reactant disposedwithin the sachet that generates a gas in the presence of an initiatingagent, wherein the envelope allows release of the gas from the envelope.2. The apparatus of claim 1 wherein the sachet comprises a materialhaving a pore size between about 0.01 μm and about 50 μm.
 3. Theapparatus of claim 1 wherein the sachet comprises a hydrophobicmaterial.
 4. The apparatus of claim 1 wherein the sachet comprises ahydrophilic material.
 5. The apparatus of claim 1 wherein the sachetcomprises a material having one or more hydrophilic zones and one ormore hydrophobic zones.
 6. The apparatus of claim 5 wherein the one ormore hydrophilic zones are created by printing an acid onto a surface ofthe sachet that is hydrophobic.
 7. The apparatus of claim 1 wherein thesachet comprises a material having a first surface that is hydrophilicand a second surface that is hydrophobic.
 8. The apparatus of claim 1wherein sachet comprises a material having a bubble point between about3 psi and about 100 psi.
 9. The apparatus of claim 3 wherein the sachethas a flow time between about 10 sec/500 ml and about 3,500 sec/500 mlfor 100% IPA at 14.2 psi.
 10. The apparatus of claim 4 wherein thesachet has a flow time between about 5 Lmh/kPa and about 500 Lmh/kPa for100% water at 14.2 psi.
 11. The apparatus of claim 1 wherein theenvelope comprises a material having a water vapor transmission ratebetween about 50 g/m²/24 hrs and about 1,000 g/m²/24 hrs.
 12. Theapparatus of claim 1 wherein the envelope comprises a material having aselective gas transmission rate of between about 500 cc/m²/24 hrs andabout 30,000 cc/m²/24 hrs for CO₂.
 13. The apparatus of claim 1 whereinthe envelope comprises a material having a selective gas transmissionrate of between about 1,000 cc/m²/24 hrs and about 10,000 cc/m²/24 hrsfor O₂.
 14. The apparatus of claim 1 wherein the reactant comprises anaqueous soluble acid and an aqueous soluble chlorite and the gas ischlorine dioxide.
 15. The apparatus of claim 14 wherein the aqueoussoluble acid is selected from the group consisting of phosphoric acid,fumaric acid, glycolic acid, acetic acid, ascorbic acid, oxalic acid,maleic acid, lactic acid, tartaric acid, citric acid and mixturesthereof.
 16. The apparatus of claim 14 wherein the aqueous solublechlorite is selected from a group consisting of sodium chlorite andpotassium chlorite and mixtures thereof.
 17. The apparatus of claim 14wherein the weight ratio of the aqueous soluble chlorite to the aqueoussoluble acid is between about 1:2 to about 1:6.
 18. The apparatus ofclaim 1 further comprising a second sachet disposed within the envelope.19. The apparatus of claim 18 further comprising a third sachet disposedabout the first sachet and the second sachet, the third sachet beingdisposed within the envelope.
 20. An apparatus for delivery of a gascomprising: a first reactant disposed within a first sachet; a secondreactant disposed within a second sachet; a third sachet disposed aboutthe first sachet and the second sachet; an envelope disposed about thethird sachet; a frangible pouch disposed within the envelope adjacent tothe third sachet; and an initiating agent disposed within the frangiblepouch, wherein the first reactant and the second reactant generate a gasin the presence of the initiating agent, and the envelope allows releaseof the gas from the apparatus.
 21. An apparatus for delivery of a gascomprising: an envelope; a partition disposed within the envelopedefining a first volume and a second volume; a first reactant disposedin the first volume; and a second reactant disposed within the secondvolume, wherein the first reactant and the second reactant generate agas in the presence of an initiating agent, and the envelope allowsentry of the initiating agent into the apparatus.
 22. An apparatus fordelivery of a gas comprising: a sachet; and a reactant disposed withinthe sachet that generates a gas in the presence of an initiating agent,wherein the sachet allows contact of the initiating agent with thereactant and release of the gas from the apparatus.
 23. The apparatus ofclaim 22 wherein the sachet comprises a hydrophobic material having apore size between about 0.01 μm and about 50 μm.
 24. A method of formingan apparatus for delivery of a gas comprising: (a) providing amulti-layer structure comprising a reactant layer centrally disposedbetween two sachet layers, and two envelope layers disposed adjacent tothe two sachet layers such that the two sachet layers are centrallydisposed between the two envelope layers; and (b) stamping themulti-layer structure such that the two envelope layers form an envelopedefined about its perimeter by the stamp, and the two sachet layers forma sachet defined about its perimeter by the stamp.
 25. The method ofclaim 24 further comprising the steps: (c) providing a second twoenvelope layers and an initiating agent in a frangible pouch; and (d)stamping the second two envelope layers to form a second envelopedefined about its perimeter by the stamp, such that the frangible pouchand the envelope formed in step (b) are disposed within the secondenvelope.
 26. A method of delivering gas: (a) providing an apparatus fordelivery of a gas comprising: an envelope, a sachet disposed within theenvelope, and a reactant disposed within the sachet that generates a gasin the presence of an initiating agent, wherein the envelope allowsrelease of the gas from the envelope; and (b) disposing the apparatus inan environment that comprises an initiating agent.
 27. The method ofclaim 26 wherein the environment is liquid and the initiating agent iswater.
 28. The method of claim 26 wherein the environment is gaseous andthe initiating agent is water vapor.